How do I Select Vertices in 2.8 Beta?
It should be left click. But, on the splash screen (screen when you open 2.8 with the galaxy picture at the top) you can change it. Mine was in right click for some reason, but I switched it. Or, you could go to user preferences (hotkey: “ctrl + ,”).

Another solution is switching the tool. In the viewport, check if your tool is the ‘select’ tool. Then you can select.

Hope it helps.